Thermal recovery techniques, in which hydrocarbons are produced from carbonaceous strata such as oil sands, tar sands, oil shales, and the like by the application of heat are becoming increasingly prevalent in the oil industry. Perhaps the most widely used thermal recovery technique involves in situ combustion or "fire flooding". In a typical fire flood, a combustion zone is established in a carbonaceous stratum and propagated within the stratum by the injection of air, oxygen enriched air or pure oxygen through a suitable injection well. As the combustion supporting gas is injected, products of combustion and other heated fluids in the stratum are forced away from the point of injection toward production zones where they are recovered from the stratum and withdrawn to the surface through suitable production wells. U.S. Pat. Nos. 3,240,270--Marx, 4,031,956--Terry, and 4,042,026--Pusch et al are examples of the recovery of oil by in-situ combustion.
In such processes, the prevention of unintended ignition due to the hazardous nature of using pure oxygen is of primary concern. For example, as the combustion zone moves away from the injection well, a large volume of unreacted oxygen sometimes accumulates near the well. If this travels upwardly in the well, a catastrophic fire possibly destroying the well, can be ignited. U.S. Pat. No. 3,125,324--Marx discusses the ignition problem. In addition, U.S. Pat. No. 4,042,026 to Pusch et al disclosed above also discusses the hazardous nature of using pure oxygen in in-situ combustion operations that could lead to uncontrolled reactions or explosions.
U.S. Pat. No. 3,240,270 to Marx discloses an in-situ combustion process for the recovery of oil in which an inert cooling fluid such as water, nitrogen, or carbon dioxide is injected into the production boreholes so as to maintain the temperature below the combustion supporting temperature at the oxygen concentration in the hole and so to prevent borehole fires.
U.S. Pat. No. 3,135,324 to Marx discloses an in-situ combustion process for recovery of oil wherein a fine dispersion of water is injected with the combustion supporting gas in a sufficient amount to maintain the temperature of the stratum around the injection well below ignition temperature.
It is an object of the present invention to provide a method and well completion for safely operating an injection well in an in-situ combustion oil recovery operation using high concentrations of oxygen.